1. Field of the Invention
This invention relates to a paper separating apparatus, especially to a paper separating apparatus having a feeding roller and a reversing roller which cooperates with the feeding roller and has a torque limiter.
2. Description of the Related Art
FIG. 5 shows a paper feeding apparatus used in an image forming apparatus such as an electrophotographic copying machine, a facsimile or a printer, such as that shown in Japanese Laid Open Patent 59-69328. A top of a bundle of paper sheets 100 in a cassette case is picked up by pick up roller 11 and fed to a separating unit. The separating unit comprises a feeding roller 10 which feeds a single (top) paper sheet in a feeding direction, and a reversing roller 2, which rotates in a direction opposite to the feeding direction, and with a predetermined torque. The reversing roller 2 cooperates with the feeding roller 10 to prevent additional sheets, other than the top sheet from being fed by the feeding roller. The reversing roller is pressed toward the feeding roller by a pressing lever 6 and a pressing spring 7. The feeding and reversing rollers are thus maintained in contact with one another, except when a sheet of paper intervenes.
After a paper sheet is separated in a nip between the feeding roller 10 and the reversing roller 2, the paper sheet is transported to the image forming apparatus (not shown) via a pair of resist rollers 8 along a guide plate 9. An image is then formed on one side or both sides of the paper sheet.
The reversing roller 2 is provided on an end of a reverse shaft 3 (FIG. 1). The other end of the reverse shaft 3 is supported so that the reversing roller 2 is movable toward the feeding roller axis. The reverse shaft is driven so as to rotate in a direction opposite to the rotating direction of the feeding roller shaft. Circlips 5 hold the rollers on their respective shafts.
A torque limiter of a clutch type is used to limit the rotating torque applied by the reverse shaft to the reversing roller to a predetermined value. As shown in FIG. 1, a conventional torque limiter comprises a spring 1a', hub 1c' and a clutch body 1b'. (The conventional torque limiter of FIG. 1 is not admitted as being prior art as defined in 35 USC .sctn. 102.) The clutch body 1b' is mounted so as to rotate integrally with the reverse axis 3, and the hub 1c' is mounted rotatably on the axis 3 and rotates together with the (separate) reversing roller via an engaging portion. The spring 1a' is disposed between the clutch body 1b' and the hub 1c'.
The clutch body 1b' and the hub 1c' have coaxial cylindrical parts which closely surround the shaft 3. The spring is wound on the coaxial cylindrical parts and so presses them onto the shaft 3 with a certain interference force and transmits torque between the clutch body and the hub. However, when the shaft 3 is rotated in the direction shown by the arrow, the corresponding rotation of the clutch body 1b' tends to unwind the spring 1a', and so reduce the interference force of the spring on the hub 1c'. The amount of torque applied by the shaft 3 onto the roller 2 can therefore be limited so that the shaft 3 can rotate without rotating the roller 2 if a force resisting the rotation of the roller exceeds the frictional force between the hub 1c' and the shaft 3.
in the conventional reversing roller described above, the number of the parts is large, and so it takes much time to assemble and maintain these parts. It is also necessary to provide the engaging portion so as to surely transmit rotation. Since a roller portion and a torque limiter portion are independently provided, it is necessary to use a long space in the axial direction.